This invention relates to an electrolytic capacitor containing a wound foil section, preferably an aluminum one, which utilizes as electrolyte a solution of 3 to 10 wt% ammonium benzoate, 4 to 16 wt% water, and 75 to 93 wt% ethylene glycol. The electrolyte has a resistivity of 385 to 620 ohm-cm and is suitable for capacitors operating above 100 V, preferably above 200 V, and above 85.degree. C., preferably 95.degree. C. and higher. A nitro compound and a phosphate may also be present.
Ammonium benzoate-ethylene glycol electrolytes have been used in capacitors for low-voltage use. These electrolytes have contained little, if any, water and relatively large amounts of solute. They are low-resistivity electrolytes and have good low-temperature properties. Amine salts of benzoic acid, particularly the tertiary aliphatic salts, have been used in electrolytes for AC motor start capacitors. They have a much higher resistivity, e.g., about 800 ohm-cm, and are suitable for the heavy duty thermal cycling conditions encountered by AC motor start capacitors. They too have contained at most minor amounts of water.
In the past, low-voltage capacitors have used low-resistivity electrolytes, e.g., 300.OMEGA.-cm or less, intermediate voltage capacitors have used intermediate resistivity electrolytes, e.g., 200-250 V capacitors have used 700-800.OMEGA.-cm electrolytes, and high-voltage capacitors, high-resistivity electrolytes, e.g., 1000.OMEGA.-cm and above.